Abstract
Most alkaloids are biologically active secondary metabolites, and accumulated in the vacuoles of plant cells. The transport mechanism of alkaloids across vacuolar membranes has, however, yet been clarified. We use cultured Coptis japonica cells as a model, since they produce high amounts of an yellowish isoquinolione alkaloid, berberine, and accumulate it in their vacuole. To clarify the molecular mechanism of the alkaloid transport across the vacuolar membrane, membrane vesicles of Coptis japonica cells were fractionated, using a discontinuous sucrose gradient. The tonoplast-enriched vesicles isolated, showed ATP-dependent [3H]-berberine uptake activity at an optimum pH of 7.5. Further characterization of berberine transport using various inhibitors of membrane transporters suggested that berberine was transported into the vacuole via a berberine/H+-antiporter.
